1. Field of the Invention
The present invention relates to a method of manufacturing a nitride semiconductor light emitting element in which a surface of the nitride semiconductor light emitting element except for a pad electrode surface is coated with a protective layer.
2. Description of the Related Art
Nitride semiconductors are generally used for light emitting elements such as light emitting diodes (LED) and laser diodes (LD), light receiving elements such as solar cells and light sensors, and electronic devices such as transistors and power devices. Especially, the light emitting diode (nitride semiconductor light emitting element) using the nitride semiconductor has been widely employed in various light sources for backlight, illumination, traffic signals, large displays and the like.
The nitride semiconductor light emitting element is formed by providing a translucent p-side whole surface electrode for uniformly diffusing a current on a p-side nitride semiconductor layer to improve an output, forming a pad electrode for wire bonding, which is made of a metal material, on the translucent p-side whole surface electrode and coating the surface except for the surface of the wire-bonded pad electrode with an insulating protective layer.
For example, JP-A-2000-174345 (refer to a paragraph 0004 and FIG. 8) describes that the pad electrode and the protective layer in such nitride semiconductor light emitting element are formed in independent different steps.
The method of manufacturing a nitride semiconductor light emitting element according to the prior art will be described with reference to FIG. 5 to FIG. 7. FIG. 5 is a flow chart showing a flow of the method of manufacturing a nitride semiconductor light emitting element according to the prior art. FIG. 6 and FIG. 7 are schematic sectional views for describing the method of manufacturing a nitride semiconductor light emitting element according to the prior art, FIG. 6A shows a state where the nitride semiconductor light emitting element is formed, FIG. 6B shows a state where a first resist pattern for forming the pad electrode is formed, FIG. 6C shows a state where a pad electrode layer is formed, FIG. 6D shows a state where the first resist pattern is removed, FIG. 7A shows a state where the protective layer is formed, FIG. 7B shows a state where a second resist pattern for exposing an electrode surface of the pad electrode is formed, FIG. 7C shows a state where the electrode surface of the pad electrode is exposed and FIG. 7D shows a state where the second resist pattern is removed.
In the method of manufacturing a nitride semiconductor light emitting element according to the prior art, as shown in FIG. 5, a nitride semiconductor light emitting element structure forming step S20, a first resist pattern forming step S21, a pad electrode layer forming step S22, a first resist pattern removing step S23, a protective layer forming step S24, a second resist pattern forming step S25, a protective layer etching step S26, a second resist pattern removing step S27 and a chip dividing step S28 are sequentially performed.
Each of the steps will be described below with reference to FIG. 6 and FIG. 7.
(Nitride Semiconductor Light Emitting Element Structure Forming Step: S20)
The method of manufacturing a nitride semiconductor light emitting element according to the prior art will be described starting from a nitride semiconductor light emitting element structure 110 shown in FIG. 6A.
The nitride semiconductor light emitting element structure 110 has a laminated structure obtained by laminating an n-type nitride semiconductor layer 111, an active layer 112 and a p-side nitride semiconductor layer 113 on a surface of a substrate 102 such as a sapphire substrate (hereinafter referred to as a wafer as appropriate). In the nitride semiconductor light emitting element structure 110, an n-side pad electrode connecting surface 110a as a region where the n-type nitride semiconductor layer 111 is exposed to connect an n-side pad electrode is formed (a left end in FIG. 6A), and an overall electrode 114 is formed on an upper surface of the p-side nitride semiconductor layer 113 to cover a substantially entire surface of the p-side nitride semiconductor layer 113.
In the present embodiment, an upper surface of the overall electrode 114 is a p-side pad electrode connecting surface 110b for connecting a p-side pad electrode, and a A-side pad electrode 122 (refer to FIG. 6D) is formed on a part of the p-side pad electrode connecting surface 110b. The nitride semiconductor light emitting element structure 110 can be formed in a publicly known manufacturing process.
A plurality of nitride semiconductor light emitting elements are formed on the substrate 102 in a matrix, and after being completed on the substrate 102, the nitride semiconductor light emitting elements are divided into chips. The example shown in FIG. 6 and FIG. 7 illustrates the process of manufacturing one of nitride semiconductor light emitting elements.
(First Resist Pattern Forming Step: S21)
Next, as shown in FIG. 6B, a first resist pattern 130 having openings in regions where the n-side pad electrode and the p-side pad electrode are formed is formed on the nitride semiconductor light emitting element structure 110 by photolithography.
(Pad Electrode Layer Forming Step: S22)
Next, as shown in FIG. 6C, a pad electrode layer 120 made of metal is formed on the entire surface of the wafer by sputtering or the like.
(First Resist Pattern Removing Step: S23)
Thereafter, by removing the first resist pattern, as shown in FIG. 6D, the first resist pattern 130 as well as the unnecessary pad electrode layer 120 laminated on the first resist pattern 130 are removed (lift-off) to form the n-side pad electrode 121 and the p-side pad electrode 122.
(Protective Layer Forming Step: S24)
Next, as shown in FIG. 7A, an insulating protective layer 123 made of SiO2 or the like is laminated on the entire surface of the wafer by sputtering or the like.
(Second Resist Pattern Forming Step: S25)
Next, as shown in FIG. 7B, a second resist pattern 131 having openings on electrode surfaces of the n-side pad electrode 121 and the p-side pad electrode 122 is formed on the surface of the wafer.
(Protective Layer Etching Step: S26)
Next, as shown in FIG. 7C, using the second resist pattern 131 as a mask, the protective layer 123 in the openings is removed by etching to expose the electrode surfaces of the n-side pad electrode 121 and the p-side pad electrode 122.
(Second Resist Pattern Removing Step: S27)
Then, as shown in FIG. 7D, by removing the second resist pattern 131, the nitride semiconductor light emitting element is formed on the substrate (wafer) 102. As described above, in this stage, the plurality of nitride semiconductor light emitting elements are arranged on the substrate 102 in a matrix.
(Chip Dividing Step: S28)
The nitride semiconductor light emitting elements arranged on the substrate 102 in a matrix are divided into chips by dicing or the like to complete the nitride semiconductor light emitting elements in units of chips.